Geochemical prospecting



Patented Jan. 20, 1942 UNITED STATE so PATENT OFFICE I az'roasa- Geochem cal. raosrnc'mzc Leo Horvitz, Houston, Tex, asslgnor to Esme E. Rosalie. Houston, Tex.

No Drawing.

Application March 23, 1939, Serial No. 263,669

'z Claims. (01. 23-232) The invention relates to prospeetingior oil, gas

and related deposits by earth sampling to -de-' termine the presence of hydrocarbons and other substances which leak or result from leakage from such deposits and which may-serve as an indication of the proximity of the deposits. 1

It has been found that the fluids which leak from the deposits become adsorbed, absorbedmcto assist in obtaining therefrom substances which are indicative of the proximity of valuable subsurface deposits.

imity to sought deposits whereas, in accordance actual soil which may be confined and subjected to treatment to .liberate the desired substances.

This method is disclosed in copending application, Serial No. 107,497, filed October 24, 1936, for Geophysical prospecting method.

In accordance with the present invention it has been found that liberation of the sought substances from the soil may be accomplished by the use of an acid or acids, particularly acids of sufficient strength to decompose whatever carbonates may be present in the soil. Thus, with the use of acid, samples may be obtained which contain a sufliciently high significant content J of sou ht gases to make the present procedure more eillcient than the method of the above noted application in which the samples may,',in some inv stances. be lean in the sought constituents.

object of the present invention is to provide an" improvement in the art of geochemical explo ration by liberating from the soil, substances which are indicative of the location of valuable subsurface deposits. V

A it is also an object of the invention to utilize an acid' in thetreatment of soil to produce. from the santiple constituents sought as an indicationoi th'e 'location of hydrocarbon deposits.

A further object of the invention is to provide a method oi obtaining gaseous samples either directly from the earth in situ or from a specimen of soil so that such samples contain a high percentage of the. significant substance which is s removably entrained in the soil. 1

Another object is to treat the soil to release in gaseous iorm the significant constituents which are in some iorm entrained therein.

Another object is to collect a gaseous sample by a process whereby the entrained constituents are 1 evolved duringor shortly before the process or taking the sampl J A still further object is to anply acid to soil These and other objects will be obvious from the present specification and appended claims.

For purposes of illustration it might be stated that when previously known technique was used in many exploration areas, the available quantity of ethane or other significant constituents in collected gaseous samples is such that-three parts ofsignificant gas per million parts of total gas sample may be considered as indicative of proxwith the present invention, a concentration of 100 or more parts of sought gas per million or total gas is obtainable in areas proximate the sought deposits. The most highly developed an? alytical equipment has a sensitivity in the order of one or two parts per million. Hence, in accordance with the invention determinations may be made from samples in which the concentra-- haye been-found to be composed of calcium cari 'tion of significant constituents is well above the threshold of apparatus sensitivity. This not only provides a technique which is more economical and practical but one in which the contour lines of isoconcentration oi significant constituents may be drawn with much higher accuracy and greater significance.

In its broadest aspect the invention includes k the step'of treating soil with an acid capable of disintegrating the carbonates in the,soil. Such action is instrumental in obtaining much richer samples of gases including significant constituents indicative of the location and extent of subterranean deposits.

In accordance with the invention it is believed at present that the acid treatment above mentioned breaks up oolites or similar bodies present in the soil. In some cases at'least, oolites are now believed to be small particles created by shells formed about gas nuclei. See, for example Science, January 13, 1939, page 27 Gas bubbles as nuclei for-oolites. Hence in accordance with this theory oolites could serve as bottles for these gas inclusions which are liberated in practicing the invention. As the oolites sofar examined bonate, the acid treatment breaks down the shell and releases the gas. While this theory is offered as an explanation of the manner of obtaining unexpected volumes of gases, it is to be underby such proposed theory.

stood that the invention is not limited or defined While the technique for practicing the invention may vary, a preferred procedure is that of obtaining soil samples in the field and transporting such samples to the laboratory for treatment whereby desired information is obtained.

An illustration of one manner of treatment of the individual samples is to first take a small portion, as for example say grams, of the sample which is examined for moisture content. A dry sample equivalent of desired weight, preferably between 50 and 150 grams, is then placed in a container for analysis. This container is sealably connected to a gas collecting device and is evacuated to about one-tenth atmosphere which is approximately the vapor pressure of the liquids in the sample. This evacuation substantially eliminates soil gases and underground air entrapped in the sample.

A suitable acid is'then added to the sample in sufficient quantity to decompose the carbonates in the sample. Any acid which will dissolve the carbonates is satisfactory and the quantity of acid used will of course depend upon the nature of the acid and the quantity of carbonates in the soilsample. When hydrochloric acid is used it has been found that from 100 cc. to 200 cc. is sufficient for treatment of a dry equivalent soil sample between 5O and 150 grams in weight.

The reaction of the acid with the sample liberates carbon dioxide and at the same time unexpectedly large quantities of hydrocarbon gases are liberated. Such liberation of gaseous products causes the pressure within the sample enclosure to rise to as much as one or more atmospheres. These products are admitted to a chamber of known volume, such chamber being partially filled with an absorbing solution such as potassium hydroxide whereby the carbon dioxide becomes absorbed.

The gaseous constituents within the chamber above the absorbing solution which may include the hydrocarbon gases will not be absorbed but remain in the chamber and may be withdrawn and analyzed whereby the objectives of the invention are realized.

It may be desirable that the sample and the acid in the soil sample chamber be additionally subjected to heat whereby entrained constituents not liberated by the reaction of the acid may be freed. Such liberation may be completed by the application of heat at about 100 C. for approximately thirty minutes.

A suitable liquid which will not readily absorb the gases may be then introduced into the soil sample chamber so that any gaseous products therein will be displaced into the sample receiving chamber with the previously collected gaseous sample. This sample is then ready for analysis to determine the amount of any or all of the hydrocarbons therein. Such analysis may comprise any of the known methods of gas analysis of sufficient accuracy to reveal the amount of hydrocarbons relative to the sample from which such constituents were obtained. It is preferred, however, that analysis be carried out in accordance with the disclosure of copending application Serial No. 183,960 filed January 8,

1938, for Means and method for analysis.- In accordance with such invention the collected gaseous sample is subjected to fractionation whereby component parts of the sample are measured as a basis for determining the proximity of soil sam- 'ples to buried deposits.

An alternative method embodying the inven- 'tion consists in penetrating the top soil for a few feet with a bore hole. Suitable collection apparatus is arranged at the mouth of the bore hole to encompass the gaseous sample liberated within the bore hole. The bottom and/or adjacent wall of the bore hole are then subjected to the action of an acid to liberate from the soil a gaseous sample which is collected within the apparatus and which is subsequently analyzed to reveal the desired information.

Another and similar manner of practicing the invention includes the step of filling the bore hole with water to replace atmospheric air and air entrapped in the adjacent soil pores. Partial or subatmospheric pressure is then applied to the collecting apparatus to draw off underground air and entrapped soil gas which are normally discarded. An acid, preferably heavier than water "is then introduced at the bottom of the hole as by a tube extending through the water to the bottom of the hole. Such acid is instrumental in liberating from the soil a gaseous sample which, due to continuation of the subatmospheric pressure, is drawn off for collection and analysis.

The invention also contemplates a technique which includes the use of an inhibited acid or an acid in solution with an inhibiting agent, some of the arsenates being suitable, so that the action of the acid is delayed for a predetermined period of time. In accordance with this modification the hole may be filled with the solution and the underground air and entrapped soil gas displaced before the liberating action on the soil occurs. -Thus the hole may be filled with the inhibited acid solution and partial or subatmospheric pressure applied to draw ofi the underground air displaced by the liquid. This air is discarded. When the action of the acid on the soil takes place liberated gaseous constituents are collected in the manner above indicated.

It is believed obvious, both from a general knowledge of chemistry and from results obtained from experiments in carrying out the invention that any acid, organic or inorganic can be used in the practice of this invention. It is preferable for obvious reasons to use an acid of which the calcium salt issoluble. It has been found generally preferable to use hydrochloric acid, but in agricultural areas where the resulting chlorides would be objectionable, field collected gas samples may be liberated by the use of nitric acid. Where the liberation of gaseous samples is accomplished on soil samples in the laboratory, hydrochloric acid is to be preferred due to its strength, and its ease of handling together with the absence of danger in case of accidental spillage.

In general the term entrained as used in the specification and claims is intended to include any gas particles which have ben bottled, ad-- sorbed, dissolved by or combined with the carbonate formations, and to distinguish from underground air and gas which is merely entrapped in the soil interstices.

The invention claimed is:

1. In the method of geochemical prospectingfor the recovery therefrorn of a gas which is analyzed for components which have resulted from the leakage of fluids from subterranean petroliierous deposits the step which comprises treating each sample with an acid to facilitate the liberation of entrained constituents therew from.

3. A method of geochemical prospecting which comprises collecting samples of soil at spaced points in an area to be explored, confining each sample in a closed space, subjecting the sample While so confined to the action of an acid capable of disintegrating the carbonates contained therein, collecting the constituents liberated in gaseous form by the reaction of acid, and analyzing the gas so collected for constituents related to subterranean petroliferous deposits.

4. A method of geochemical prospecting which comprises collecting 'soil samples at spaced points in an area to be explored, treating each sample with an acid while reducing the pressure on said sample and heating it, collecting the constituents liberated in gaseous form by the reaction of the acid and the applied heat, ,and analyzing I the gas so collected for -constituents related to subterranean. petroliierous deposits.

5. A method according to claim 2 in which the acid employed is hydrochloric acid.

6. A method according to claim 4 in which the acid employed is hydrochloric acid.

'7. In the method of geochemical exploration the process of withdrawing from the soil the underground air and entrapped gaseous constituents contained therein and discarding such gases, subjecting the soil to the action of an acid capable of dissolving the carbonates contained therein, whereby gases adsorbed on the soil particles and. contained in an occluded state within the carbonate particles are liberated, and analyzing the evolved gasesfor hydrocarbons and their derivatives which indicate the proximity of subterranean petroliferous deposits.

' LEO HORVITZ. 

